A fuel cell comprises a cathode, an electrolyte and an anode. The cathode is supplied with an oxidizing agent, for example, air, and the anode is supplied with a fuel, for example hydrogen.
Different fuel cell types are known, including for example, the SOFC fuel cell of the publication DE 44 30 958 C1 and the PEM fuel cell of the publication DE 195 31 852 C1.
The SOFC fuel cell is also known as a high-temperature fuel cell since its operating temperature can be up to 1000° C.
At the cathode of a high-temperature fuel cell oxygen ions are formed in the presence of the oxidizing agent. The oxygen ions traverse the electrolyte and recombine on the anode side with the hydrogen arising from the fuel to water. With the recombination, electrons are liberated and thus electrical energy is generated.
A plurality of fuel cells as a rule are electrically connected to one another by connecting elements and are mechanically joined by interconnectors with one another for producing greater electrical outputs. An example of a connecting element is the bipolar plate. By means of bipolar plates, fuel cells are stacked one upon another and connected electrically in series. This arrangement is known as a fuel cell stack. A fuel cell stack is comprised of the bipolar plates and the electrode-electrolyte units.
Interconnectors generally also serve as gas distributor structures apart from their electrical and mechanical characteristics. In the bipolar plates the gas distributor structures are realized by ribs with electrode contacts which separate the gas passages to supply the electrodes (DE 44 10 711 C1). Gas distributor structures ensure that the operating media are uniformly distributed in the electrode compartments (compartments in which the electrodes are found). The following problems can arise with fuel cells and fuel cell stacks:                Metallic bipolar plates with a high chromium content form conductive chromium oxide cover layers;        in operation there is an evaporation of chromium resulting in ageing characteristics within the fuel cell.        Metallic bipolar plates with high aluminum content form Al2O3 cover layers which act detrimentally like an electrical insulator.        In a fuel cell stack, between the known rigid bipoplar plates and the electrode-electrolyte units, poorly conducting contact points can arise. These can arise from fabrication tolerances in the production of bipolar plates or electrode-electrolyte units.        